This invention relates to a shaft structure of a golf club and a method of producing the shaft and, more particularly, a fiber reinforced plastic golf club shaft and its producing method.
In these days, there has been widely known a golf club shaft made of a carbon fiber reinforced plastic material which has a superior strength, a high elastic or modulus property and a light weight in comparison with a metallic golf club shaft. A golf ball can be sent with a long flying distance by striking the ball with a golf club shaft formed of a carbon fiber reinforced plastic material in comparison with the metallic golf club shaft, but the carbon fiber reinforced shaft is insufficient in torsion, so that the ball struck with the carbon fiber reinforced plastic golf club shaft may fly in a direction different from that desired and it is also difficult to impart a spin to the ball by striking the ball with the carbon fiber reinforced plastic golf club.
Furthermore, recently, there has been also widely known a golf club having a shaft formed by winding different kinds of fibers such as carbon or graphite fibers, amorphous metallic tapes or metallic fibers in multiple layers to improve the torsional rigidity and the flexural rigidity of the shaft of the golf club.
However, in the conventional shafts of the golf clubs of the type in which the amorphous material or metallic material other than the carbon or graphite material is solely wound as an outer layer for the golf club shaft, the outer layer is liably easily peeled by the impact or torsion applied to the golf club shaft when the golf club strikes a golf ball. For this reason, the layer made of the amorphous material or the metallic fiber is only wound as an inner layer for the golf club shaft. In an example in which the metallic fiber is wound as the inner layer, however, the location of the metallic fiber prevents the inner and outer layers from being tightly contacted or engaged with each other. In order to obviate this defect, it is possible to wind the metallic fiber around the golf club shaft in a spiral fashion or a twill fashion with suitable angles. However, the conventional golf club shaft is basically formed by the inner layer constructed as a .theta..degree.-angled layer having an cutting angle of .+-..theta. (30.degree. to 45.degree.) and the outer layer constructed as 0.degree.-angled layer with respect to the axial direction of the shaft. In order to improve torque, i.e., the torsional rigidity, of the golf club shaft, it is, however, known to be advantageous to construct the inner and outer layers as the .theta..degree.-angled layers. In this view point, the conventional golf club shaft in which the outer layer is constructed as .theta..degree.-angled layer is not provided with a desired torsional rigidity for the reason described above.